Geographical Distribution

This disease is endemic in most areas of the world but is very common in the tropics where control of animals is limited. A few island countries are free of the disease.

Causative Agent

The disease is caused by an RNA virus of the rhabdovirus group which has a long incubation period.

Transmission

The major source of infection is through the bite of an infected animal. Any warm blooded animal may be capable of transmitting the disease through their infected saliva. A few cases of airborne transmission have been reported. Congenital transmission is known to occur in some animals but human cases have not be shown. Again injestion of infected meat has been known to cause the disease in animals but not man. Human to human spread is possible in theory but has not been reported to date. All ages are at equal risk.

Disease Cycle

Following an infected bite the virus is placed under the skin surface. Here the virus multiplies for a period of days or weeks. It then travels along the peripheral nerves and via the axons to the dorsal root ganglia. Here further multiplication of the virus occurs. The virus passes to the central nervous system and is capable of passing from cell to cell. The final path of its journey takes it back along axons to the salivary glands and many other deep organs eg heart, skeletal tissue, kidney, cornea etc. The extent of the viraemia caused is minimal. By escaping into the saliva the virus is transmissible to another host through inoculation. Anywhere between 3 days and 3 years. Most commonly between 1 to 3 months. The incubation period is directly related to the extent of the inoculation and the closeness of the brain. Thus bites on the face and neck are particularly significant and will, in general, be associated with a short incubation period.

Symptoms & Signs

In many patients no symptoms occur until the final days of the disease are reached. The site of the initial inoculation will usually have fully healed and be well forgotten. When the patient begins to experience the first effects of the disease frequently they will experience fever and headaches. They then may relate a numbness at the site of the original bite. The ankle is the most common site. Following this patients complain of anxiety, photophobia and muscular pains. Patients may then fall into one of two categories;

Furious Rabies: This is the most common variety (80%). The patients experience severe muscular spasms which may lead to apnoea, if the respiratory muscles are involved. The patients tend to develop spasm of the pharyngeal muscles which is precipitated by swallowing, cold drafts across the neck or movement. The fear of swallowing leads to an unwillingness to swallow their own saliva (hydrophobia) and saliva continually drips from the corners of their mouth.

Paralytic Rabies: Less common variety in man. Death may be delayed but always occurs. Patients tend to lie quietly and because of the gross hypersalivation, saliva dribbles from their mouths. Some patients with furious rabies may have periods of paralytic symptoms.

Diagnosis & Treatment

There is no firm way of making the diagnosis before the symptoms/signs first appear. Corneal impression smears may be of some value early into the symptomatic stage of the disease showing the virus by antibody techniques. Serodiagnosis is only of value after the appearance of signs, when no therapy can be instigated. Post mortum diagnosis (for animals or man) can be made by taking cerebral tissue and finding the typical Negri bodies and an encephalomyelitis. Only supportive humanitarian measures are available; Valium Analgesia Intravenous fluids Atropine

Prophylaxis

This is the most important aspect of dealing with rabies from a human point of view. The prophylactic regimes vary from centre to centre. In most areas a human diploid vaccine is used (HDCV) or a vero vaccine. In many of the developing countries the older animal vaccine is used with its inherent risks.

Pre Exposure Vaccination: Rabies (HDCV) may be used to confer antibody protection to individuals before they are infected. The vaccine is given on two to three occasions over a 1 to 4 week period. This is believed to provide excellent cover but treatment should always be sought if there’s any concern of exposure.

At the time of Exposure: The bite should be well washed with water to remove as much saliva as possible from the area. If soap is used at this stage it must be well washed off before an antiseptic is applied to the area. The area should then be covered and the patient should have post exposure vaccination as soon as possible.

Post Exposure Vaccination: ALL PATIENTS MUST OBTAIN SPECIALISED MEDICAL ATTENTION AND THE NOTES BELOW SHOULD ONLY BE USED AS AN OUTLINE.

Active and passive immunisation can be used. In severe proximal bites both should be administered as soon as possible following inoculation. The hyperimmune serum (passive) can be injected mainly at the site of inoculation and whatever is left by the intramuscular route separate to where the active vaccine is to be administered. The vaccine (HDCV) is given by the intramuscular route on days 0, 3, 7, 14, 30 and 90. It is a very effective vaccine but the cost limits it use in the developing parts of our world where transmission is highest. In these areas it has been shown that by using the intradermal route effectiveness can be reached without the immense costs involved.

Comments

Numerous attempts are going on throughout the world to lessen the spread of this horrific disease. The major upsurge in Europe recently has been associated with the spread of the disease by foxes. Any warm blooded animal can carry the virus. Almost all are themselves killed by the disease and so following a bite if the animal survives a period of 10 days it may be taken that it was not rabid at the time of the bite.

WHO Recommendations: 2002

Rabies post-exposure treatment

In a rabies-endemic area, the circumstances of an animal bite, other contact with the animal, and the animal’s behaviour and appearance may suggest that it is rabid. In such situations, medical advice should be obtained immediately. Post-exposure treatment to prevent the establishment of rabies infection involves first-aid treatment of the wound followed by administration of rabies vaccine and antirabies immunoglobulin in the case of class 3 exposure. The administration of vaccine, and immunoglobulin if required, must be carried out, or directly supervised, by a physician. Post-exposure treatment depends on the type of contact with the confirmed or suspect rabid animal, as follows:

Type of contact (class of exposure)

Recommended treatment

• 1 / Touching or feeding animals, Licks on the skin
  None
• 2 / Nibbling unbroken skin, Minor scratches without bleeding, Licks on broken skin
  Administer vaccine immediately (1)
• 3 / Single or multiple bites or scratches with skin penetration, Contamination of mucous membrane by saliva from licking
  Administer antirabies immunoglobulin and vaccine immediately

First-aid treatment

Since elimination of the rabies virus at the site of infection by chemical or physical means is the most effective mechanism of protection, immediate vigorous washing and flushing with soap or detergent and water, or water alone, is imperative. Following washing, apply either ethanol (70%) or tincture or aqueous solution of iodine or povidone iodine.

Specific treatment

Antirabies immunoglobulin (RIG) is applied by instillation into the depth of the wound and by infiltration of the surrounding tissues. As much as possible of the total RIG volume required should be instilled into the wound. Vaccine (2) is applied by intradermal or intra-muscular injection in schedules requiring several doses (4 or 5 doses by intramuscular injection, depending on the vaccine used), with the first dose being administered as soon as possible after exposure and the last dose within 28 days for intramuscular or 90 days for intradermal vaccination.

Patients who have been vaccinated prophylactically against rabies with a full course of cell-culture or duck-embryo vaccine can be given a shorter course of post-exposure treatment with fewer doses; they do not require RIG. Urgent post-exposure treatment remains essential whether or not patients have been previously vaccinated.

1 Treatment can be stopped if the suspect animal is shown by appropriate laboratory examination to be free of rabies or, in the case of domestic dogs and cats, if the animal remains healthy throughout a 10-day observation period.

2 Modern rabies vaccines, made from cell-culture or duck-embryo-derived rabies virus which is then purified and inactivated, are replacing the older vaccines produced in brain tissue.